controlling a stepper with a simple trigger switch

[routercnc]

If you really want to move the CNC machine independant of a PC then you can in theory connect a function generator to one of the step/pulse inputs to a BOB. It would move the motor at the speed set by the function generator. Select square wave, ~5v output, frequency set to give the required speed. For direction you need to supply 0v or 5v to the direction pin.

If you do this you probably need to isolate the PC parallel port temporarily to avoid putting 5v into an output.

I believe this is essentially what the MPG does but it goes through the software to retain position.

If you go direct you are bypassing Mach/Linux so I think it would completely loose position.

Perhaps a macro would be a better option assigned to a spare button on an MPG.